The present invention relates to an apparatus which permits an improvement to the carburetion of internal combustion engines and which is fitted between a multibody carburettor and the induction manifold of an internal combustion engine.
Such an apparatus serves to improve the carburetion of internal combustion engines by increasing the homogeneity of the air/gasoline mixture supplying the various cylinders, thus ensuring a better distribution of this mixture and consequently permitting a sufficient reduction in the richness of the mixture to bring about a significant reduction of unburnt material, hydrocarbons and carbon-monoxide as well as a significant decrease in the specific consumption.
In the case of mutli-cylinder engines supplied by a carburettor, studies have shown that the composition of the mixture which effectively supplies each cylinder is subject to significant differences compared with the composition of the mixture from the carburettor. These differences are mainly due to the heterogeneity of the mixture from the carburettor, the flow being of the two-phase type with a liquid phase and a gaseous phase whereby during its transfer into the induction manifolds the bends and different configurations of the latter aid a segregation of the suspended droplets, thus contributing to the formation of a liquid film flowing in an uncertain manner. All these phenomena have the effect of causing significant differences in richness between the mixture which actually enters each cylinder and that which leaves the carburettor. Moreover, it is known on an experimental basis that the mixture supplying a cylinder must have a minimum richness to function normally. This richness R is often called "the richness limit for stable operation" and has for its minimum value with commercial gasoline: R=0.70 ##EQU1##
This minimum richness increases at partial loads because under these conditions the dilution of the mixture carburetted by the residual exhaust gases becomes larger.
Thus, in the case of multi-cylinder engines supplied by a carburettor the mixture from the latter must have a richness which is sufficient to enable the cylinder receiving the least rich mixture to have a richness which exceeds the "richness limit for stable operation". Thus, any distribution fluctuation makes it necessary to regulate the complete engine assembly relative to the least rich cylinder and experience has shown that with conventional induction manifolds it is not possible to sufficiently reduce the richness of the mixture to obtain significant reductions of unburned pollutants, hydrocarbons and carbon-monoxide.
Many processes have been proposed for solving this problem.
According to certain processes the intake manifold is heated by the exhaust gases to bring about the vaporisation of the gasoline which streams down, thus improving the distribution.
According to other processes, baffles or deflectors are located in tanks heated directly or indirectly by exhaust gases in order to firstly separate the non-vaporised fractions and secondly their vaporisation.
These processes improve the distribution of the mixture to the different cylinders under stable operating conditions but their design is such that they lead to latent delivery defects under transient operating conditions, e.g. acceleration and deceleration, as well as to serious difficulties during starting and cold operation. The described processes and apparatuses have in fact either hollows or tanks in which the fuel tends to concentrate during cold starts and accelerations, thus causing a sudden reduction in the richness of the mixture which is prejudicial to the good operation of the engine.
Moreover, the design of the apparatuses used for applying these processes is such that during its passage into the inside thereof the mixture undergoes a significant temperature rise, thus causing a decrease in the mass filling of the engine at full load, resulting in a power loss. This power loss is increased through these systems having high pressure drops for the mixture flows required for full load.
To illustrate the prior art, reference is made to the following patents in their chronological order of filing which relate to processes having one or more of the defects indicated hereinbefore.
U.S. Pat. No. 1,490,921(1924), describes a system in which the air/fuel mixture from the carburettor undergoes a complete change in direction relative to a spherical plate heated by the exhaust gases. This system has a hollow and leads to an excessive temperature of the mixture.
French Pat. No. 807,185(1936) describes a system in which the air/fuel mixture from the carburettor is rotated by a baffle in the form of an endless screw in such a way that heavy particles are projected and directed into channels heated by the exhaust gases. The presence of hollows leads to an instantaneous reduction in the richness of the mixture during acceleration.
French Pat. No. 955,606(1947) describes a system in which the air/fuel mixture from the carburettor is rotated in the same way as in the previously mentioned patent but both the walls and baffle are kept at a relatively high temperature by the exhaust gases and a tank is provided for storing the non-vaporised portion. The apparatus has hollows and heats excessively the carburetted mixture.
U.S. Pat. No. 3,146,768(1964) describes an apparatus comprising a so-called pre-induction chamber located downstream of a carburettor in which a certain volume of exhaust gases is added to the mixture and the resulting mixture is given several complete direction changes by baffles which locally give the mixture a centrifugal movement. In view of its design, this apparatus has numerous hollows in which the fuel is concentrated and which can be associated with a tank for storing the fuel. This apparatus causes an excessive pressure loss at full load.
U.S. Pat. No. 3,421,313(1974) describes an apparatus similar to that described in U.S. Pat. No. 3,146,768. The mixture is centrifugally displaced by the introduction of exhaust gases and by the baffle. As in the previously mentioned patent, this apparatus has a hollow.
U.S. Pat. Nos. 2,259,993 and 2,259,995(1975) describe an apparatus in which the mixture undergoes at least one complete direction change with the object of bringing about the impact of the non-vaporised fractions on a heated plate. Impact takes place in a so-called hot box of small dimensions. Another important characteristic in combination with the main constructional principle is to provide the discharge apperture of the box in the pipe of the induction manifold at a point which is axially aligned with that where the secondary body of the carburettor supplies the induction manifold.
In view of its design, this apparatus has a hollow which causes no delivery defect for transient operating conditions but which can cause problems during starts at low temperature and with a cold engine.
Reference is finally made to French Patent Application No. EN 7434012 entitled "Process and apparatus permitting an improvement of the carburetion of internal combustion engines" filed in the name of the present Applicant which describes a process comprising directing the heterogeneous air/gasoline mixture leaving the carburettor to at least one centrifugal separator or cyclone in which the gasoline droplets undergo a centrifugal movement, the walls of the cyclone are heated so as to cause the vaporisation of part of the droplets, the remaining droplets are collected in a collecting chamber directed towards a vaporiser or the fuel tank, forced back into the mixing circuit and the thus homogenised gas is delivered to the combustion chamber.
The apparatus used for applying this process comprises at least one homogeniser for connection downstream to a carburettor, and upstream to the combustion chamber, whereby the homogeniser is a cyclone having an intake pipe for the air/gasoline mixture from the carburettor, a mixing cone having, for example, fixed vanes which gives a centrifugal movement to the air/gasoline mixture, a discharge pipe for said mixture issuing into the combustion chamber, a collecting chamber in which are collected the non-vaporised gasoline droplets, a pipe for transferring the gasoline droplets to a vaporiser and a pipe for transferring the vaporised gasoline into the air/gasoline mixture circuit.
Finally, according to the First Certificate of Addition No. EN 75 23354 the above apparatus was improved by modifying the cyclone in such a way that it has no obstacle which can oppose the direct flow of the air/gasoline mixture to the induction manifold, so that it has no hollow and in addition the cyclone is externally heated in such a way as to ensure the complete vaporisation of the droplets.